<p>Please please please don’t fret over one B. Been there, done that. </p>
<p>It is true that when faced with two similar applicants in all other aspects, a college will most likely choose the person who has a better _______ (in your case GPA), but I highly doubt that even a school like Caltech would look at an application and be like, “Oh, this person got one B in physics. They must be really dumb. Let’s reject them!”</p>